Has turned into wood (3)
I believe the answer is:
ash
'wood' is the definition.
(wood from an ash tree)
'has turned' is the wordplay.
'turned' is an anagram indicator.
'has' anagrammed gives 'ASH'.
'into' acts as a link.
(Other definitions for ash that I've seen before include "Remains from the yule-log?" , "Grey colour" , "Residue of burnt matter" , "Variety of tree" , "Remains of conflagration" .)